The development of effective vaccines for intracellular microbial pathogens, such as mycobacteria, toxoplasma, plasmodium, and leishmania, remains an elusive goal. Despite substantial efforts to define the mechanisms required for resistance, develop new adjuvants, and identify protective antigens, the long-lived cellular immunity generated in response to pathogen infection cannot always be recapitulated by vaccination. Leishmaniasis is an important neglected tropical disease that occurs worldwide, caused by several different parasites, for which no vaccine is available. However, both mice and humans who have resolved a primary infection with leishmania are highly resistant to reinfection. We discovered that leishmania immune mice contain a population of skin resident T cells, which we believe could be a key factor in their resistance. In this exploratory R21 we propose to fully characterize these T cells, in order to determine if they will be an important component in a successful leishmanial vaccine. Based upon our finding, we propose two specific aims that will advance our understanding of skin resident T cells and provide a foundation for new immunization approaches for the disease. In Aim 1 we will determine whether the skin localized T cells are indeed bona fide resident memory T cells in the skin and will assess what contributes to their maintenance in the skin. We will also directly determine their role in immunity, by transferring them into the skin of nave mice followed by challenge experiments. In Aim 2, we will take advantage of the observation that vaccinia virus immunization by skin scarification induces a robust skin resident T cell population. We will immunize mice with vaccinia virus expressing a protective leishmanial antigen, thiol-specific anti-oxidant. These studies will evaluate the resident memory T cells present, compare them with those generated by infection, and determine if they provide protective immunity. Taken together, these are the first studies to evaluate the role of skin resident T cells in immunity to any intracellular microbial pathogen, and will provide new information about skin resident T cells that can be applied to vaccine development.